Optical Properties,Self-assembly Functions And Mechanism Of Solvent-controlled Azobenzene Derivatives

A supermolecular self-assembled structure is a stable aggregation of a specific framework and function spontaneously,formed by one or more molecules through intermolecular non-covalent weak interactions.The non-covalent interactions mainly include electrostatic interactions,?-effects,Van der Waals interactions and Hydrophobic effects.Supramolecular self-assembled structure has the ability to respond to external stimuli,including magnetic fields,electric fields,and light.Under external stimuli,it also causes obvious changes in physicochemical characteristics,such as: the color change of self-assembled structure,the movement and changes of fluorescence peak position and intensity,the collapse of self-assembly system,and in-situ chemical bond compounding.These unique,tunable features allow them to have a good prospect of application in various fields such as brakes,sensors,cell/drug transportation systems,tissue engineering and regenerative medicine.Among the supramolecular assembled,there are a lot of common structures.For example: self-assembling surfaces/films,gels,nanoparticles/clusters/tubes,and so on.The small molecule gel based on supramolecular self-assembly has attracted more and more attention based on its advantages such as easy availability of raw materials,simple production process and easy regulation of properties.In this work,the gel behavior,transparency,photoresponsive behavior,self-healing ability and intermolecular interaction mechanism of azobenzene derivatives from solvent regulation were studied systematically.we obtained the gel with special photoresponsive behavior,high transparency and autonomic self-healing by the regulation of poor solvent,.The molecular interaction mechanism in the self-assembly system was studied by means of experiments and the analysis of the Hansen solubility parameters.In addition,BNB-t4 self-healing gel has many applications such as removing toxic dyes,adhering on solid surfaces and self-supporting.Details are follows:1.From the gelation studies of BNB-tn(n = 1,2,4 and 8)in various single and binary solvents,we found that the optical properities of BNB-t4 self-assembled structure were successfully regulated,with the introduction of a second solvent cyclohexane.(1)The BNB-t4 gel in the 50:50 chloroform/cyclohexane(TCM/CYH)mixture demonstrates a high transparency closing to 100%,have a special photoresponsive behavior.(2)Under the regulation of cyclohexane,the photoisomerization process of azobenzene derivatie also undergoes a continuous change.First,we studied the effect of mixed solvent on the photoresponssive behavior of BNB-t4 from the low concentration monomolecular state.The isomerization degree of BNB-t4 was increased by adding cyclohexane properly.At a high concentration,BNB-t4 gel factors produce aggregates,because the difference of aggregates in different proportions leads to differences in the response behavior of aggregates to light.2.The self-assembly behavior of cyclohexane-regulated BNB-t4 gel,self-healing behavior and other applications were systematically studied.(1)The experimental results showed that the gel ability,thixotropic properties and self-repair properties of BNB-t4 organogels were effectively regulated by adding the content of cyclohexane in chloroform/cyclohexane mixed solvent.(2)Under the condition of chloroform/cyclohexane 50:50,the gel ability and self-repair ability of BNB-t4 reached the best value.The mechanical properties of self-healing gels revealed by rheological tests show that proper introduction of cyclohexane can greatly improve the thixotropic properties and mechanical stability of BNB-t4.(3)In addition,BNB-t4 self-healing gel has many applications such as removing toxic dyes,adhering of solid surfaces and self-supporting.3.Based on the above studies on the properties of BNB-t4 gel,we also analyzed the molecular interaction mechanism in the self-assembly system according to the experimental test and calculation.(1)The temperature dependent transparency and morphology studies indicate that the high transparency of the BNB-t4 gel originates from the aggregate size of nanoscale fibres.(2)Based on the results from NMR,FTIR,and UV-vis spectral measurements,the cyclohexane regular the strength modulation of intermolecular hydrogen bonding interactions.(3)Furthermore,the spectral results and analysis using Hansen solubility parameters demonstrate that the hydrogen bonding interactions through the amide and hydroxyl groups of BNB-t4 mainly contribute to the regulation of gelation ability and properties,on the premise of a weak polar interaction and moderate dispersion force.Synthetically,the hydrogen-bonding interactions coupled with the ?–? stacking interaction through the azobenzene group and van der Waals interactions via alkyl chains are responsible for the regulated self-assembly behaviors and properties of the BNB-t4 gel in TCM/CYH mixtures.The success in achieving the BNB-t4 gel shows an effective strategy to achieve the specific properties of organogels through regulating specific solubility parameters.